Method for coating metal anodes with electroconductive paint

ABSTRACT

A method for coating metal anodes with electroconductive paint including the provision of a cylinder with a large enough volume of paint to coat an entire continuous surface of an anode, and delivering the paint from the cylinder to the anode at a constant and non-pulsating rate by the single displacement stroke of a piston in the cylinder.

Krause et al.

1451 Sept. 16, 1975 [54] METHOD FOR COATING METAL ANODES 2,785,088 3/1957 Ransburg 239/3 X 3,040,992 6/1962 W1cgand 417/316 X 3,144,831 8/1964 Pickels et a.I.... 417/429 X 1 n ntors: J n z J ef Henryk Kr D vi 3,169,883 2/1965 Juvinall 239/15 x Alan Denton, both of Runcorn, 3,512,502 5/1970 Drum 239/15 X E la d 3,784,335 1/1974 Cevera 417/429 X [73] Assignee: Imperial Chemical Industries FOREIGN PATENTS OR APPLICATIONS Limited, London, England 1,147,442 4/1969 United Kingdom [22] Filed: Jan. 24, 1974 Primary Examiner-M. Henson Wood, Jr. [21] Appl 436349 Assistant ExaminerAndres Kashnikow Attorney, Agent, or FirmCushman, Darby & [30] Foreign Application Priority Data Cushman Feb. 2, 1973 United Kingdom 5237/73 [57] ABSTRACT 2% 427/33; 5;5 :153 A method for coating metal anodes with electrocomd M26 3 l 6 ductive paint including the provision of a cylinder with l 1 2 7 3 22 {T1367 4 A 93 2 a large enough volume of paint to coat an entire con- 93 2 tinuous surface of an anode, and delivering the paint from the cylinder to the anode at a constant and nonpulsating rate by the single displacement stroke of a [56] References Cited piston in the cylinder.

UNITED STATES PATENTS 1,250,474 12 1917 L60 417/521 13 Clams 1 Draw'ng F'gure 17 I9 /2 I6 /.9 l6 /0 ACTH/9 T0R1" PATENTEDSEP 1 61975 3,908,122

ACTl/A TOR-J" METHOD FOR COATING METAL ANODES WITH ELECTROCONDUCTIVE PAINT The invention relates to coating of metal anodes with electroconductive paint.

The application of paint to a surface of an object by spraying from an air atomization spray gun is a well known technique, but can lead to substantial losses of paint owing to a carry over of paint in the air flow into regions outside the actual area to be coated.'These losses are especially important when using expensive paints, e.g. the electroconductive paints used in the coating of titanium anodes for use in mercury cells. Such losses may be substantially reduced by the use of an electrostatic spraying technique in which the charged paint droplets are attracted to the object to be sprayed. In a conventional electrostatic spray gun, for example, the paint is fed to a gun charged at a high positive potential where it is atomized (e.g. by air pressure or by centrifugal action), and the .object to be coated is grounded. It is important, however, to deliver paint to the spray gun at a steady and controllable rate in order to ensure that the object is uniformly coated with paint. Moreover, the uniformity of deposition of the paint may be adversely affected byleakage of electrical charge from the gun, which in turn affects the spraying characteristics of the gun. It is therefore important to provide adequate electrical insulation of the paint spraying system, especially when using electroconductive paints because of their electrical conducting properties.

In practice, a uniform steady flow of paint is not readily achieved. The use of a gravity feed of paint, for example, is unsatisfactory because of variations in flow associated with variations in the head of the paint being fed to the spray gun and because of possible pressure drops in the delivery system. The use of diaphragm pumps is unsatisfactory because of the pulsating nature of the feed. A more positive and efficient metering device is desirable and accordingly we have designed an apparatus which ensures the positive displacement of a predetermined amount of paint to the gun in a smooth and continuous manner, and which is to a large extent independent of pressure drop in the delivery system.

According to the present invention we provide a method for spraying a predetermined amount of paint at a controlled uniform rate which comprises in combination an electrostatic spray gun and a paint delivery device for the gun which operates on a piston and cylinder principle.

In a preferred apparatus for practicing the present method the cylinder of the delivery device is provided with an inlet for introducing paint thereto, and an outlet through which the paint is delivered to the gun, the said inlet and outlet being provided with independently operable valves. The piston is associated with an actu ating means for moving said piston within the cylinder, whereby paint is introduced into the cylinder on one stroke of the piston (with the inlet valve open and the outlet valve closed) and paint is discharged on the opposite stroke of the piston (with the inlet valve closed and the outlet valve open). Any conventional actuating means may be used, for example a mechanical actuating means such as a screw jack, or a hydraulic actuating means, for example a hydraulic cylinder coupled to the piston by means of a suitable linkage. The actuating means, whether mechanical or hydraulic, may itself be actuated electrically, mechanically or pneumatically. Suitable arrangements include a screw jack or a hydraulic cylinder in association with a variable speed drive electric motor.

The apparatus may suitably include one or more piston and cylinder devices for delivering the paint in conjunction with one or more actuating means and one or more electrostatic spray guns. In a preferred arrangement, the apparatus comprises two electrostatic spray guns, each with its own piston and cylinder delivery device, the said delivery devices being associated with a single actuating means. When using a single actuating means in combination with a plurality of delivery devices and their associated guns, it will be understood that one setting of the actuating means enables each of the guns to operate at the same flow rate.

In practice, it is preferred to fill a delivery device rapidly with paint, while discharging the said paint at a controlled, predetermined and usually slow, rate. The delivery device may be advantageously used to meter accurately very small flows such as l to 10 ml/minute, for example 1 to 5 ml/minute. The spraying may conveniently be operated in a batchwise manner by adjusting the rate of delivery to correspond to the overall spraying time required. The operation of any one delivery device including the opening and closing of the valves, or of a plurality of such deliverydevices, may be fully automated if desired.

The electrostatic spray gun(s) and the object to be sprayed are conveniently moved relative to one another. It is especially convenient to move the object at constant rate transverse to the electrostatic spray gun.

An embodiment of the invention will now be described, simply by way of example, with reference to the accompanying drawing which is a schematic representation of two electrostatic spray guns in association with two piston and cylinder devices for delivering paint.

Referring to the drawing, the apparatus for practicing the present method comprises two electrostatic spray guns 1, 2 in combination with two piston and cylinder delivery devices (designated generally as 3, 4). Each gun I, 2 is provided with a rotating hell (not shown) for atomizing paint delivered to the gun and is connected to a high voltage supply (I-IV) for charging the gun to a suitably high electric potential relative to an electrode 25 to be sprayed, which electrode is grounded. Each delivery device 3, 4 comprises a closed cylinder 5, 6 in which moves a piston 7, 8. The cylinders 5, 6 are respectively provided with inlets 9, 10 for introduction of paint thereto, the said inlets 9, 10 being connected via valves 11, 12 and a common pipe 13 and valve 14 to a head vessel 15 for paint. Cylinder 5 is further provided with an outlet 16 for delivery of paint which connects via valve 17 to the head of gun 1. Cylinder 6 is further provided with an outlet 18 for delivery of paint which connects via valve 19 to the head of gun 2. The pistons 7, 8 are connected respectively by rods 20, 21 to a bridge member 22, which is in turn connected via rod 23 to an actuator 24. The actuator 24 may be of any suitable type such as one of a wide variety of conventional hydraulic or mechanical actuators. Operation of the actuator causes upwards or downwards movement of the bridge member 21, which in turn causes the pistons 7, 8 to move upwardly or downward respectively in cylinders 5, 6.

In use, a paint is introduced into the head vessel 15 with valves 11, 12 and 14 in their closed position. Valve 14 is opened, followed by valves 11 and 12. The actuator 24 is operated to lower the pistons 7, 8 within cylinder 5, 6, thereby drawing paint into the said cylinders. The valves 11, 12, and 14 are then closed and the valves 17 and 19 opened. The actuator 24 is then operated to raise the pistons 7, Sat a definite rate, thereby delivering to the guns 1, 2 the desired amount of paint in the desired time (e.g. at the rate of l to ml/minute).

It will be appreciated that when an electroconductive paint is used, it is necessary to insulate the rods 20, 21 and the bridge member 22, so that the actuating system is electrically isolated from the paint containing system. In practice, the head vessel 15, the pipes 9, 10, 13, 16 and-18, the guns 1, 2, and the cylinders 5, 6 and pistons 7, 8 are all charged to a potential of 100 kV, rods 20, 21: and the bridge member 22 are insulated, and the rod 23 and the actuator 24 are at ground potential.

The invention is especially applicable to the spraying of electroconductive paints, e.g. the electroconductive paints used for coating of titanium anodes for use in electrolytic cells. Preferred coatings include platinum, platinum/iridium alloys, platinum group metal oxides, particularly ruthenium oxide, and especially mixtures of platinum group metal oxides and film-forming metal oxides, for example ruthenium oxide and titanium dioxide. The platinum metal coatings may be formed, for example, by electrodeposition on the film-forming metal, for example as described in UK. Patent No. 1,237,077. Platinum group metals and their conducting compounds, particularly oxides, are readily produced by the thermal decomposition techniques, as described for example in UK. Patent Nos. 1,147,442; 1,195,871;

1,206,863 and 1,244,650.

The invention is further illustrated by the following Example.

Example Two electrostatic spray guns were arranged, one above the other, so that the one gun was directed on the top half of a titanium anode (14 in X 10.5 in) and the other gun was directed on the bottom half. An electroconductive paint composition, consisting of ruthenium trichloride and an organic titanium compound dissolved in an alcohol, was fed at the rate of 3 ml/minute to each of the guns. At the same time, the titanium anode was moved transverse to the paint sprays at the rate of 1 ft/minute. After spraying, the anode was fired at 180C to remove the alcohol and then at 450C to thermally decompose and oxidize the paint constituents to give a coating consisting of a mixture of ruthenium oxide and titanium dioxide. The spraying and firing operations were repeated several times to give the desired thickness of electroconductive coating.

What we claim is:

l. A method of coating metal anodes with electroconductive paint comprising the steps of a. providing an electrostatic spray gun at a high electrical potential,

b. providing a cylinder containing a predetermined volume of electroconductive paint, said volume of paint in said cylinder being large enough to coat an entire continuous surface of a metal anode to be coated,

c. placing a continuous surface of a metal anode to be coated in position to receive electroconductive paint from said spray gun,

d. ensuring that said metal anode to be coated is at ground potential,

e. positively delivering electroconductive paint from said cylinder to said spray gun at a continuous nonpulsating rate by the single displacement stroke of a piston in said cylinder, and

f. spraying said delivered electroconductive paint from said spray gun onto said anode surface at said continuous non-pulsating rate thereby providing delivery of a sufficient volume of electroconductive paint from said cylinder to said continuous metal anode surface to completely and uniformly coat said surface.

2. A method as recited in claim 1 wherein said paint is delivered to said spray gun and is sprayed from said spray gun onto said anode at a constant rate of between 1 and 10 ml/minute.

3. A method as recited in claim 2 wherein said rate is between 1 and 5 ml/minute.

4. A method as recited in claim 1 comprising the further step of transversely moving said metal anode continuous surface to be coated relative to said spray gun.

5. A method as recited in claim 4 wherein said rate of movement of saidanode with respect to said spray gun is l fL/minute.

6. A method as recited in claim 1 wherein the predetermined volume of paint in said cylinder is enough to coat a plurality of continuous anode surfaces during the single displacement stroke of said piston in said cylinder, and wherein said method comprises the further step of consecutively bringing a plurality of grounded metal anode continuous surfaces into position to receive paint from said gun.

7. A method as recited in claim 1 comprising the further steps of, after the volume of paint in 'said cylinder has been depleted, preventing delivery of paint from said cylinder to said spray gun, providing for communication between'said cylinder and a paint reservoir, and withdrawing the piston in said cylinder .and thereby simultaneously providing for the intake of another predetermined volume of electroconductive paint from said reservoir into said cylinder, whereby said method may be repeated.

8. A method of coating metal anodes with electroconductive paint comprising the steps of a. providing a plurality of electrostatic spray guns at a high electrical potential,

b. providing a plurality of cylinders, one associated with each of said spray guns and each .containing a predetermined volume of electroconductive paint, the combination of said volumes of .paint in said cylinders being large enough to coat an entire continuous surface of a metal anode to be coated,

c. placing a continuous surface of a metal anode to be coated in position to receive paint from said spray guns,

d. ensuring that said metal anode to be coated is at ground potential,

e. positively delivering electroconductive paint from said cylinders to said spray guns at a continuous nonpulsating rate by the single displacement stroke of a piston in each of said cylinders, and

f. spraying said delivered electroconductive paint from said spray guns onto said anode surface at said continuous non-pulsating rate thereby providing delivery of a sufficient volume of electroconductive paint from said cylinders to said continuous metal anode surface to completely and uniformly coat said surface.

9. A method as recited in claim 8 wherein said electroconductive paint is delivered to said spray guns and is sprayed from said spray guns onto said anode at a constant rate of between 1 and 10 ml/minute.

10. A method as recited in claim 9 wherein said rate is between 1 and 5 ml/minute.

11. A method as recited in claim 8 comprising the further step of transversely moving said metal anode continuous surface to be coated relative to said spray guns.

12. A method as recited in claim 8 wherein the combination of said predetermined volumes of electroconductive paint in said cylinders is large enough to coat a plurality of anode surfaces during the single displacement stroke of a piston in each of said cylinders, and wherein said method comprises the further step of consecutively bringing a plurality of grounded metal anode continuous surfaces into position to receive paint from said spray guns.

13. A method as recited in claim 8 comprising the further steps of, after the volume of paint in said cylinders has been depleted, preventing delivery of paint from said cylinders to said spray guns, providing for communication between said cylinders and a paint reservoir, and withdrawing the piston in each of said cylinders and thereby simultaneously providing for the intake of electroconductive paint from said reservoir into said cylinders, whereby said method may be repeated. 

1. A METHOD OF COATING METAL ANODES WITH ELECTROCONDUCTIVE PAINT THE STEPS OF A. PROVIDING AN ELECTROSTATIC SPRAY GUM AT A HIGH ELECTRICAL POTENTIAL, B. PROVIDING A CYLINDER CONTAINING A PREDETERMINED VOLUME OF ELECTROCONDUCTIVE PAINT, SAID VOLUME OF PAINT IN SAID CYLINDER BEING LARGE TO COATED AN ENTIRE CONTINUOUS SURFACE OF A METAL ANODE TO BE COATED, C. PLACING A CONTINUOUS SURFACE OF A METAL ANODE TO BE COATED IN POSITION TO RECEIVE ELECTRONDUCTIVE PAINT FROM SAID SPRAY GUM, D. ENSURING THAT SAID METAL ANODE TO BE COATED IS AT GROUND POTENTIAL, E. POSITIVELY DELIVERING ELECTROCONDUCTIVE PAINT FROM SAID CYLINDER TO SAID SPRAY GUM AT A CONTINUOUS NON-PULSATING RATE BY THE SINGLE DISPLACEMENT STROKE OR A PISTON IN SAID CYLINDER, AND F. SPRAYING SAID DELIVERED ELECTROCONDUCTIVE PAINT FROM SAID SPRAY GUM ONTO SAID ANODE SURFACE AT SAID CONTINUOUS NON-PULSATING RATE THEREBY PROVIDING DELIVERY OF A SUFFICIENT VOLUME OF ELECTROCONDUCTIVE PAINT FROM SAID CYLINDER TO SAID CONTINUOUS METAL ANODE SURFACE TO COMPLETELY AND UNIFORMLY COAT SAID SURFACE.
 2. A method as recited in claim 1 wherein said paint is delivered to said spray gun and is sprayed from said spray gun onto said anode at a constant rate of between 1 and 10 ml/minute.
 3. A method as recited in claim 2 wherein said rate is between 1 and 5 ml/minute.
 4. A method as recited in claim 1 comprising the further step of transversely moving said metal anode continuous surface to be coated relative to said spray gun.
 5. A method as recited in claim 4 wherein said rate of movement of said anode with respect to said spray gun is 1 ft./minute.
 6. A method as recited in claim 1 wherein the predetermined volume of paint in said cylinder is enough to coat a plurality of continuous anode surfaces during the single displacement stroke of said piston in said cylinder, and wherein said method comprises the further step of consecutively bringing a plurality of grounded metal anode continuous surfaces into position to receive paint from said gun.
 7. A method as recited in claim 1 comprising the further steps of, after the volume of paint in said cylinder has been depleted, preventing delivery of paint from said cylinder to said spray gun, providing for communication between said cylinder and a paint reservoir, and withdrawing the piston in said cylinder and thereby simultaneously providing for the intake of another predetermined volume of electroconductive paint from said reservoir into said cylinder, whereby said method may be repeated.
 8. A method of coating metal anodes with electroconductive paint comprising the steps of a. providing a plurality of electrostatic spray guns at a high electrical potential, b. providing a plurality of cylinders, one associated with each of said spray guns and each containing a predetermined volume of electroconductive paint, the combination of said volumes of paint in said cylinders being large enough to coat an entire continuous surface of a metal anode to be coated, c. placing a continuous surface of a metal anode to be coated in position to receive paint from said spray guns, d. ensuring that said metal anode to be coated is at ground potential, e. positively delivering electroconductive paint from said cylinders to said spray guns at a continuous nonpulsating rate by the single displacement stroke of a piston in each of said cylinders, and f. spraying said delivered electroconductive paint from said spray guns onto said anode surface at said continuous non-pulsating rate thereby providing delivery of a sufficient volume of electroconductive paint from said cylinders to said continuous metal anode surface to completely and uniformly coat said surface.
 9. A method as recited in claim 8 wherein said electroconductive paint is delivered to said spray guns and is sprayed from said spray guns onto said anode at a constant rate of between 1 and 10 ml/minute.
 10. A method as recited in claim 9 wherein said rate is between 1 and 5 ml/minute.
 11. A method as recited in claim 8 comprising the further step of transversely moving said metal anode continuous surface to be coated relative to said spray guns.
 12. A method as recited in claim 8 wherein the combination of said predetermined volumes of electroconductive paint in said cylinders is large enough to coat a plurality of anode surfaces during the single displacement stroke of a piston in each of said cylinders, and wherein said method comprises the further step of consecutively bringing a plurality of grounded metal anode continuous surfaces into position to receive paint from said spray guns.
 13. A method as recited in claim 8 comprising the further steps of, after the volume of paint in said cylinders has been depleted, preventing delivery of paint from said cylinders to said spray guns, providing for communication between said cylinders and a paint reservoir, and withdrawing the piston in each Of said cylinders and thereby simultaneously providing for the intake of electroconductive paint from said reservoir into said cylinders, whereby said method may be repeated. 